Unreduced catalyst for ammonia synthesis and process for its manufacture

ABSTRACT

A catalyst for ammonia synthesis having a high catalytic activity and good physical-chemical characteristics is prepared by gradually melting an iron bar above a steel crucible cooled on the outside with water. The melting is carried out uninterruptedly over a period of 16 minutes by directing onto the melting end of the bar an oxygen stream, e.g. at a pressure of 0.15 atm. An oxidizing melting reaction of the iron occurs which being exothermal has the effect of raising the temperature. The ferrous oxide flows into the crucible and concomitantly are added the promoters, i.e. Al2O3, K2CO3, SiO2, CaO. An inhomogeneous fluid mass results. The crucible is then closed and oxygen is fed in, producing inside the crucible (over a period of 3 minutes) a pressure of 2 kg/sq cm. Feeding of oxygen is then stopped and the crucible is immediately discharged. The molten mass is cooled, crushed, sized and packed.

United States Patent Stefanescu et al.

UNREDUCED CATALYST FOR AMMONIA SYNTHESIS AND PROCESS FOR ITS MANUFACTURE lnventors: Constantin Stefanescu; Ion

Vartolomei; Gheorghe Urziceanu; Gheorghe Badea, all of Craiova, Romania Combinatul Chimic Craiova, Craiova, Romania Filed: Aug. 18, 1971 Appl. No.: 172,895

Related U.S. Application Data Continuation-in-part of Ser. No. 806,737, March 12,

Assignee:

'1969, abandoned.

References Cited UNITED STATES PATENTS 12/1968 Hinrichs et al. 252/472 [451 Aug. 28, 1973 3,644,216 2/1972 Egalon et al. 252/455 R Primary Examiner-C. F. Dees Attorney-Karl F. Ross A catalyst for ammonia synthesis having a high catalytic activity and good physical-chemical characteristics is prepared by gradually melting an iron bar above a steel crucible cooled on the outside with water. The melting is carried out uninter'ruptedly over a period of 16 minutes by directing onto the melting end of the bar an oxygen stream, e.g. at a pressure ofO. l 5 atm. An oxidizing melting reaction of the iron occurs which being exothermal has the effect of raising the temperature. The ferrous oxide flows into the crucible and concomitantly are added the promoters, i.e. A1 0 K,CO SiO,-, CaO. An inhomogeneous fluid mass results. The crucible is then closed and oxygen is fed in, producing inside the crucible (over a period of 3 minutes) a pressure of 2 kg/sq cm. Feeding of oxygen is then stopped and the crucible is immediately discharged. The molten mass is cooled, crushed, sized and packed.

ABSTRACT 5 Claims, No Drawings 1 UNREDUCED' CATALYST FOR AMMONIA SYNTHESIS AND PROCESS FOR ITS MANUFACTURE- CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of our copending application Ser. No. 806,737, filed=on Mar. 12', 1969' (now abandoned), replaced by application Ser'. No. 86,311 of Nov. 2, 1970, also abandoned.

FIELD OF THE INVENTION- The present invention relates to an unreducedcatalyst for ammonia synthesis and to-a process for its manufacture.

BACKGROUND OF THE INVENTION Many catalysts, and processes for making same, are known for ammonia synthesis. Each ofthehithertoknown types of catalyst has'one or another of the following disadvantages: hygroscopi'city, poor mechanical resistance, long reduction time's, partial or total loss of catalyst activity at high operating temperatures, low efficiency and poor productivity. Basically, the prior-art processes for manufacturing the ammonia-synthesis catalysts make use of oxidizing meltingof special iron to magnetite with addition of promoters, and melting of natural or synthetic magnetite together with'promoters' in electrical furnaces-with or without-introduction of steam. I

The drawbacks of these methods and of their several variants reside in that they cannot produce a perfectly homogeneous mixture of the magnetite and the respective promoters; the result is a detrimental influence on the physieo-chemical characteristics and on the catalytic activity of the catalysts.

OBJECT OF THE INVENTION It is an object of this invention to provide an improved nonreduced catalyst, andmethod of making same, for ammonia synthesis.

SUMMARY OF THE INVENTION oxygen medium, which effects an intensive ebullition,

or bubbling of the fluidized mass under the influence of the heat evolved from the oxidation reaction nd promotes simultaneously secondary chemical reaction between the iron oxides and the promoters.

According to another feature of the invention, the promoters are the following: 3.3 percent by weight of the iron body to 4.2% Al,0, (1.2-1.5 kg per 36kg iron), 1.4 to 2.25% K,CO, (0.5-0.8 kg), to l.4% SiO, (0-0.5 kg), and 0 to 6.66% CaO (0-2.4 kg). Advantageously the lower limit for both the silicon dioxide and lime is 0.35 percent, always by weight.

The process, acco'rdingto theinvention, uses 0.15 kgf/sq cm oxygen for the mild oxidizing melting of iron to ferrous oxide, at a temperature between l,530 and l,727 Centigrade, according to the principal reaction:

Fe A 0 Feo 64.4 kcal.

The mild oxidizing melting is carried out, in known apparatus, uninterruptedly over a period of 16 minutes, until the entire'body of iron intended for the respective charge isconsumed, concomitant with the introduction in small portions of the promoters, which may be two to four in number, using dosage recipes known per se.

The next stepof the process is carried out in the case of a 36 kg' iron body, according to the invention, over a period'of 3 minutes at'a pressure of 2 kgf/sq. cm., the molten ferrous oxide being oxidized quickly and violently in an oxygen atmosphere, according to the principal reaction:

3 FeO 1% 0 Fe O 72 kcal.

Owing to the reaction heat, a temperature of between 1,369C and 2,000C is developed, which fluidizes the molten mass, in an excessive agitation stae and promotes homogenization, as well as secondary reactions between the iron oxides and the metal oxides introduced as promoters in the first step.

SPECIFIC EXAMPLES The preparation of a tetrapromoter catalyst for ammonia synthesis is illustrated by the following examples:

EXAMPLE I:

The end of an iron bar is heated by means of an autogenous-welding burner up to 1,500C. At this temperature, the mild oxidizing melting of the iron is started by directing a 0.15 kgf/sq cm oxygen current onto the melting end of the bar, the temperature rising to 'l,727 C by virtue of the exothermal reaction. The ferrous oxide in the molten state flows into a steel crucible, cooled on the outside by water, where, owing to the heat exchange, it begins to cool. For one charge, 36 kg of iron are uninterruptedly melted during a period of I6 minutes, concomitantly with the progressive introduction into the melt ot'; the following amounts of promoters: Alzog 1.5 kg; Co K2 0.8 kg; Si0 0.5 kg and CaO 2.4 kg. A semi-fluid nonhomogeneous mass results. The crucible is closed and oxygen is .fed in, raising the pressure within the crucible from 0.15 kg/cm? to 2 kg/sq cm pressure during a period of 3 minutes. Feeding of oxygen is then stopped and the crucible is immediately tipped over. The molten mass cools down, is crushed, sorted and packed.

The results given below are of experiments made in a commercial plant, provided with a Ul-IDE type syn thesis column, wherein the catalyst made as described above is placed in tubes, the gas having five paths; in this plant-it was not possible to obtain fully optimum conditions because the gas rate of flowof the compressors was insufficient owing to thehigh activity of the catalyst tested.

Ammonia synthesis achieved with the catalyst prepared according to the invention:

(a) Heating Period Rate of flow of recycled gas m'/h(S.T.P.) 5.000 Catalyst amount cubic meters 0.216 Operating temperature C 560 Operating pressure atmosphere 240 2S0 Ammonia percentage at inlet of the column I 2.68 Ammonia percentage at outlet of the column k 100 12,88 Efficiency NHJV eg.) 100 69% Mean ammonia production/day tons 14.5 Productivity (tons Nhl lm catal.)/24 h 67 EXAMPLE I] The process of Example I was carried out, but neither SiO nor CaO were employed. The results were substantially the same.

EXAMPLE/Ill Once again the process was identical to that given above except that the following quantities of the four promoters were used:

1.2 kg A1 0 0.5 kg K CO 0.3 kg SiO and 1 kg CaO. The results also were substantially equivalent with those given above.

The catalyst, according to this invention, presents the advantage that it is not hydroscopic and does not need to be packed hermetically, it is resistant to compression (85 kgf/granule), and it has a high thermal stability.

We claim:

1. A method of making an unreduced catalyst for the synthesis of ammonia in a reduced state, comprising the steps of:

continuously melting an iron body in the presence of only sufficient oxygen to form ferrous oxide from the melt by melting an iron bar continuously and uninterruptedly by directing against the melting bar a stream of oxygen and concomitantly mixing the ferrous-oxide melt with 3.3 percent by weight to 4.2% Ai,o,, 1.4% to 2.25% x co 0% to 1.4% SiO, and 0% to 6.66% CaO, and thereafter rapidly oxidizing-the mixture under an oxygen pressure to convert the ferrous oxide at least in part to ferric oxide while inducing ebullition of the mixture. 2. The method defined in claim 1 wherein said stream of oxygen has a pressure of about 0.15 kgf/cm.

3. The method defined in claim 2 wherein the molten ferrous oxide is oxidized in a crucible under an oxygen pressure of substantially 2 kg/cm.

4. The method defined in claim 3 wherein said body is melted at a temperature of substantially l,727 Centigrade and said mixture is oxidized at a temperature of at least l,369 Centigrade.

5. A method of making an unreduced catalyst for the synthesis of ammonia in a reduced state, comprising the steps of:

continuously melting at a temperature up to about 1,727C an iron body in the presence of only sufficient oxygen at a pressure of about 0.15 kg/cm to form ferrous oxide from the melt and concomitantly mixing the ferrous-oxide melt with at least two ammonia-synthesis-catalyst promoters selected from the group consisting-of A1 0 K,CO SiO, and CaO; and thereafter rapidly oxidizing the mixtureunder an oxygen pressure of substantially 2 kg/cm and at a temperature of at least about l,369C to convert the ferrous oxide at least in part to ferric oxide while inducing ebullition of the mixture, all four of the members of said group being added during the oxidizing melting of said iron bar in the proportion of 1.5 kg A1 0,, 0.8 kg K CO 0.5 kg SiO and 2.4 kg CaO per 36 kg of the iron bar.

i l i =8 i 

2. The method defined in claim 1 wherein said stream of oxygen has a pressure of about 0.15 kgf/cm2.
 3. The method defined in claim 2 wherein the molten ferrous oxide is oxidized in a crucible under an oxygen pressure of substantially 2 kg/cm2.
 4. The method defined in claim 3 wherein said body is melted at a temperature of substantially 1,727* Centigrade and said mixture is oxidized at a temperature of at least 1,369* Centigrade.
 5. A method of making an unreduced catalyst for the synthesis of ammonia in a reduced state, comprising the steps of: continuously melting at a temperature up to about 1,727*C an iron body in the presence of only sufficient oxygen at a pressure of about 0.15 kg/cm2 to form ferrous oxide from the melt and concomitantly mixing the ferrous-oxide melt with at least two ammonia-synthesis-catalyst promoters selected from the group consisting of Al2O3, K2CO3, SiO2 and CaO; and thereafter rapidly oxidizing the mixture under an oxygen pressure of substantially 2 kg/cm2 and at a temperature of at least about 1,369*C to convert the ferrous oxide at least in part to ferric oxide while inducing ebullition of the mixture, all four of the members of said group being added during the oxidizing melting of said iron bar in the proportion of 1.5 kg Al2O3, 0.8 kg K2CO3, 0.5 kg SiO2 and 2.4 kg CaO per 36 kg of the iron bar. 